Thank you very much for your answer and for the suggestion to change document security settings.

I asked already development team to implement this change, but I'm afraid this may not help.
I generated a similar PDF document but from another program, where different HTML2PDF convert was used.
The security settings are exactly the same ... but in this case Ranorex Spy works perfect. I attached an example.

In this case, there is probably something wrong with the PDF exported from that other tool? Another thing you can try is to play a bit with the Accessibility settings in Adobe Reader (menu Edit >> Accessibility). But this may not help either. Good luck!